Machines for freezing and dispensing a soft confectionery product such as frozen custard, milk shakes, or soft ice cream generally include a freezing cylinder housing a rotary dasher. Positioned above the freezing chamber is a reservoir containing a suitable mix in the form of a liquid product which, when subsequently frozen under proper conditions, will yield the desired flavor and texture. The dasher in the freezing chamber acts to whip air into the mix as well as circulate the product within the freezing chamber so as to assure reasonably uniform temperature, texture, and the like.
The freezing chamber and liquid product reservoir are typically connected in some manner so as to permit a suitable amount of new liquid product to move from the reservoir to the freezing chamber at the same time as some frozen product is being dispensed from the freezing cylinder. In the machines to which this invention applies, the freezing chamber and the liquid product reservoir are typically connected by an open tubular communicating line extending between the two. An element may be positioned near the liquid product reservoir end of the tubular communicating line to control the amount of mix and air which is drawn into the freezing chamber. A common failing of machines of this type has been the inability of the machines to obtain the proper "over-run" in the dispensed product. The term "over-run" refers to the amount of air by volume which is added to the liquid mix.
When the frozen product is not being dispensed from the freezing cylinder, the machine must periodically cycle on and off so as to correctly maintain the temperature and texture of the frozen product in the freezing chamber. When the machines cycles on, the beater or dasher also runs in order to keep the frozen product firm enough so it can be dispensed when needed. As the machine remains in this "standby" condition for any extended period of time, the resultant frozen product, when finally dispensed, will not contain as much air as it should, and as a result will lack proper taste, not stand up in a cone, and often becomes grainy. Soft ice cream normally dispensed from an apparatus of this type is most desirably served at 17.degree. F. to 20.degree. F. with a 3 to 5% butterfat mix content and an "over-run" of at least 50%. Typically, however, a gravity-fed machine of this type not utilizing the advancement of this invention will average significantly below 50% over-run. Solutions have been suggested to this problem of maintaining the "over-run" in the frozen product, including the use of elaborate pumps for introducing pressurized or compressed air into the freezing chamber. Examples of machines using an external air pressurizing device are to be found in U.S. Pat. No. 3,196,633, U.S. Pat. No. 3,147,601, and U.S. Pat. No. 2,565,121. The disadvantage of the addition of such elaborate pumping schemes is the increased energy which is required to run the apparatus, problems in mechanical failure, valuable time consumed in cleaning, as well as the non-convertibility of most older types of gravity-fed machines.
Other solutions have involved the use of systems for metering the introduction of liquid product into the freezing chamber based upon an electromagnetic interaction with the dispensing valve of the freezing chamber. Examples of machines using devices of this type are to be found in U.S. Pat. No. 2,737,024, U.S. Pat. No. 3,196,637, U.S. Pat. No. 3,304,737, and U.S. Pat. No. 3,866,801. Again, these devices have the disadvantage of an increased energy consumption, although much smaller than the elaborate pumping schemes previously referred to. Many of the devices require substantial modification of existing machines, and as a result, many older type gravity-fed machines are, again, not convertible to this type of product manipulation.